Check legal stuff

[jkbe]

Licenses for images, fonts as well as imprint + "Datenschutzerklärung" etc.

[flowirtz]

@jak-ing Updated the imprint, image sources are also referenced there.
Can you have a look what else needs to be checked and if done close this? Thanks!
Done from my side, see #4 #39

[jkbe]

Seems to be fine.